[PATCH 21/27] ext4: implement zero_range iomap path

Zhang Yi
2024-10-22T03:13:05Z

From: Zhang Yi <yi.zhang@huawei.com>

Introduce ext4_iomap_zero_range() to implement the zero_range iomap
path. Currently, this function direct invokes iomap_zero_range() to zero
out a mapped partial block during the truncate down, zeroing range and
punching hole. Almost all operations are handled by iomap_zero_range().

One important aspect to consider is the truncate-down operation. Since
we do not order the data, it is essential to write out zeroed data
before the i_disksize update transaction is committed. Otherwise, stale
data may left over in the last block, which could be exposed during the
next expand truncate operation.

Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
---
fs/ext4/inode.c | 25 +++++++++++++++++++++++++
1 file changed, 25 insertions(+)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 34701afe61c2..50e4afd17e93 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -4147,6 +4147,13 @@ static int __ext4_block_zero_page_range(struct address_space *mapping,
return err;
}

+static int ext4_iomap_zero_range(struct inode *inode, loff_t from,
+ loff_t length, bool *did_zero)
+{
+ return iomap_zero_range(inode, from, length, did_zero,
+ &ext4_iomap_buffered_write_ops);
+}
+
/*
* ext4_block_zero_page_range() zeros out a mapping of length 'length'
* starting from file offset 'from'. The range to be zero'd must
@@ -4173,6 +4180,8 @@ static int ext4_block_zero_page_range(struct address_space *mapping,
if (IS_DAX(inode)) {
return dax_zero_range(inode, from, length, NULL,
&ext4_iomap_ops);
+ } else if (ext4_test_inode_state(inode, EXT4_STATE_BUFFERED_IOMAP)) {
+ return ext4_iomap_zero_range(inode, from, length, did_zero);
}
return __ext4_block_zero_page_range(mapping, from, length, did_zero);
}
@@ -4572,6 +4581,22 @@ int ext4_truncate(struct inode *inode)
goto out_trace;

ext4_block_truncate_page(mapping, inode->i_size, &zero_len);
+ /*
+ * inode with an iomap buffered I/O path does not order data,
+ * so it is necessary to write out zeroed data before the
+ * updating i_disksize transaction is committed. Otherwise,
+ * stale data may remain in the last block, which could be
+ * exposed during the next expand truncate operation.
+ */
+ if (zero_len && ext4_test_inode_state(inode,
+ EXT4_STATE_BUFFERED_IOMAP)) {
+ loff_t zero_end = inode->i_size + zero_len;
+
+ err = filemap_write_and_wait_range(mapping,
+ inode->i_size, zero_end - 1);
+ if (err)
+ goto out_trace;
+ }
}

if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))
--
2.46.1